Virtually every modern plant or factory has one form or another of article conveying means which are substantially automatic and independent of operator control. Conveyors may be overhead carriers, pneumatic tubes, horizontal rollers, chairs or belts. The simplest conveyors were, and are, one piece, sewn, continuous leather or fabric belts. The present invention, however, relates to conveyors having flat, horizontal, narrow plates or links, hinged, one behind another and which are driven over pulleys. Being linked to one another, the conveyors, themselves, are frequently referred to as "chains" and will hereinafter be so called.
There are essentially two types of flat, horizontal, articulated conveyor chains in use today. One conveyor is straight running, where the entire conveyor belt or chain is pulled in one straight line, over a pulley which is a drive sprocket, and then drawn back in a straight line to the starting point, which is an idler sprocket. Drive sprockets are arranged to pull the linked plates, as distinguished from pushing them. This type of chain will convey articles only in a linear path.
Two straight running conveyors running essentially at right angles to each other is called a butt turn.
A second type of articulated link conveyor is the side flexing chain, or, as it is also called, "flex chain". Each thin flat plate is not only articulated by being hinged to the adjacent plates, but is capable of pivoting or sideflexing relative to the straight path, such that the chain itself can go around a curve. Of necessity, the curves have large radii and require more space to make a right angle turn than two straight running conveyors arranged at right angles to each other. The flex chain needs a greater degree of maintenance and requires the use of lubricant because of the friction between the chain and wear strips which support it as well as the friction between the upper or supportive surface of each chain plate and the articles carried on them. In the flex chain system, the links are subject to arcing or pivotal motion relative to one another as the flex chain goes around a curve.
Flex chains are more expensive, heavier, and have additional bulk on their bottom or non-article supporting surfaces to follow in a track in the conveyor frame. On the positive side, flex chains produce a smoother "ride" for articles conveyed at relatively high speed. One reason for this is that they go around large radius curves.
The article engaging surfaces of both straight running and side flexing chains are generally thermoplastic material hinged with stainless steel pins. Many are nominally 71/2 inches wide.
The present invention relates to single file chains which produce a butt turn or a dead turn, wherein two separate conveyor chains are arranged essentially at right angles to one another. Articles may be conveyed by such chains either single file or in mass flow where there are a number of conveyed articles abreast of one another. Because articles are constantly pivoting and rotating on the upper or support surfaces of the flex chain plates, large quantities of conveyor lubricant is needed. Not only is the lubricant potentially a contaminant to any food or beverage which is being placed in the article being conveyed such as bottles or cans, but the cost of disposing of effluence associated with spent conveyor lubricant is ever increasing.
One of the requirements for successful material handling is to maintain stability of conveyed articles to a very high degree. Instability is generally a function of the size and relative weight of the articles being conveyed. For example, large rectangular cartons packed with filled cans rarely tip over unless there is a complete conveyor breakdown. However, articles such as unfilled plastic bottles with high centers of gravity and low weight per volume ratios are quite susceptible to tipping. Even the bottles, when filled, being relatively tall in proportion to their bases can tip and spill their contents.
On a straight running conveyor, stability of an article is influenced by the articles contact with the chain, contact with the guide rails, and contact with other containers. While moving in a straight path, there is little contact with the guide rails. Consequently, there is little influence on their velocity which remains substantially constant. Anything that contacts an article, as by friction, influences its velocity and consequently reduces its stability. Contact with guide rails when making a turn is unavoidable. However, since most turns are made with articles such as bottles moving in single file, as for example, with a single infeed chain and a single discharge chain, when the articles are not being conveyed single file, they invariably touch one another which reduces stability.
New developments in materials for conveyor chains have been aimed at lowering friction and ultimately running without conveyor lubricant. This is obviously a benefit because of the ever increasing cost of effluent discharge associated with used conveyor lubricant and other waste lubricants. However, chains being manufactured with new materials, for the most part, are of the straight running type and not flex chain. This means that turns must be accomplished by the older method of butt turns rather than flex turns.
In the conventional butt turn, when a article, such as a container, enters a turn, it contacts a guide rail, generally curvilinear, but not necessarily so. It consequently decelerates in the direction of movement of the infeed chain, but is displaced by the guide rail at an angle generally-approaching that of the discharge chain, which, for the most part, is oriented at right angles to the infeed chain. As the article continues through the curve, it continues to decelerate in the direction of the infeed and to pick up an ever increasing component of movement toward the discharge chain.
As an article being conveyed nears completion of the turn, velocity in the infeed direction approaches zero. However, the velocity in the direction of the discharge chain also approaches zero because it is still on the infeed chain. As an article, such as a bottle or other container, reaches the end of its contact with the guide rail, the guide rail in effect becomes a barrier or tangent to any further motion in the infeed direction while the infeed chain drags across the bottom of the then almost stationary container. The deceleration or change in velocity contributes to its instability.
It is to these problems that the present invention is directed.